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Fun Post Bulletin newspaper facts
07-14-2018, 05:03 AM (This post was last modified: 07-14-2018 05:05 AM by Ron.)
Post: #1
Fun Post Bulletin newspaper facts
Submitted by John Weiss.

For years, I had a water thermometer hanging from my trout vest because … well, because the experts had thermometers hanging from their vests.

Today, however, I get it. A water thermometer can be a guide to when and where I fish for trout and other species — or if I should fish at all.

It all began on a hot day last summer when I was trout fishing the Root River in Preston. Fishing was abysmal, and I really wasn’t thinking about water temperature. My logic? Trout are cold-water species, so if the trout were there, the water must be cold. Simple and obvious.


For some reason, I decided to use my thermometer — 68 degrees.

I was shocked. I went home and did some research, learning that when water is that warm, trout stop feeding heavily, and if caught, can die from the stress even if handled correctly.

The thermometer also helped last weekend. I fished the North Branch Whitewater River, and fishing was slow. Water was 66 degrees.

I checked the Middle Branch in Whitewater State Park and it was the same.

But the smaller, more pristine, Trout Run Creek enters the river in the park. I checked that creek — 52 degrees and much clearer. Below the confluence the river was about 62-63 degrees. Fish were biting.

Water temperature and fishing, however, are not simple, said Doug Dieterman, a Department of Natural Resources fisheries researcher in Lake City. “It gets real complicated really quick,” he said, because there are so many factors that go into when fish feed. Temperature is just one of them.

Let’s begin with the basics, he said. There are three kinds of fish around here: cold-water species such as trout; cool-water species such as walleye, sauger, northern, crappie and perch; and warm-water species such as bluegills and bass. Each has its own prime temperature range when they feed the best, gain the most weight and females produce the most eggs. Go beyond it, and they begin to shut down, or even die.

Here are the prime feeding/growth ranges (sweet spots) followed by the temperature where they stop growing and finally, the one that will kill them in a week (all are given in Fahrenheit):

• Trout: 54 to about 60, 63-66, 72-78.

• Walleye/sauger: 67-73, 75, 84-86.

• Northerns: 63-70, 75, 82.

• Crappies: No optimal listed; 81-84, 88.

• Bluegills: 69-75, 79-81; 85-90.

• Smallmouth: 65-79, 84-85, 85-95.

• Largemouth: 66-79, 90-93, 90-97.

While actual kills are rare, they do happen.

There was a major heat-related kill of big walleye on Lake Pepin in 2012, and the biggest northerns in Silver Creek Reservoir also died because of high water temperatures that year.

In bodies of water where fish have a cooler-water refuge, usually a deeper place, they can survive, Dieterman said. But Pepin, being part of the Mississippi River, has no refuges except where cooler streams enter the lake. And Rochester’s reservoirs, except for Chester Woods, aren’t deep.


What effect the warming climate is having on fish is not well known, Dieterman said. “We are still in the data-gathering phase,” he said. But one part of climate change is more precipitation, and some of that filters down into bedrock and comes out in springs that are 48 degrees. With more spring flow, some streams seem to be getting a bit cooler, he said.

Those extra springs have more than doubled the number of miles of trout streams in our region, from about 300 miles in the 1970s to about 800 miles today, he said.

Nick Schlesser, the DNR large-lake specialist for Pepin, said there is one more factor anglers need to think about — hooking mortality. As water gets warmer, walleye, even if caught and quickly released correctly, stand a much higher chance of dying from the stress. Once out of that sweet spot, “you are adding stress to the fish,” he said.

Whether you should fish when water temperatures are high is up to you. “I’m not in charge of other people’s ethics,” he said. “That’s kind of an individual call.”

The hardest thing in life is knowing which bridge to cross and which one to burn.
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Thanks given by:  Tom
07-14-2018, 08:37 AM
Post: #2
RE: Fun Post Bulletin newspaper facts
Interesting things to consider.

I've carried a stream thermometer for crappie fishing for so many years I don't think the one I use is available any more. I know I've replaced the tether string at least 10-12 times and get at least 4 years use from the cord.

More crappie related to this article in our local waters, higher water temps can promote fungal/bacterial growth that can affect age/size specific fish. White bass are another that can be at issue. I've seen on Lake Zumbro several such fish kills where crappies in the 4-6 inch size range died off in huge numbers but didn't adversely affect any others. I've seen white bass go thru the same thing on the lake. Low flow rates and higher than normal heat trends seemed to be a couple of the key factors when these events occurred.

Algae blooms have always plagued the Zumbro with agricultural run-off being very high at times when lots of rain has been happening. If memory serves me correctly there have been a few water-use warnings in the past regarding swimming and allowing dogs to use the water when the blooms are happening.

Water temperature can help determine where fish are not going to be found and much as where they will be found and as John and the DNR point out high water temperatures can also simply not be good for the fishes health even if the fish are released quickly. On a more positive note though, having a thermometer allows one to check water temps at different depths other than that given by a transducer hung on a transom or stuck on the bottom of the boat. There are times of the year when water temps on the surface and that found as little as a down can determine whether you'll be in the fish or not.
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